Desenvolvimento de método de preparo de amostras para determinação de sódio, potássio, cálcio e magnésio em leite de manejo orgânico e convencional por espectrometria de emissão atômica com chama (F AES) e espectrometria de absorção atômica com chama (F AAS)

Abstract

In this study a method was developed for the determination of the macrominerals Na, K, Ca and Mg in different types of milk (raw, UHT, pasteurized and powdered), from organic and conventional management, using the techniques of Flame Atomic Emission Spectrometry (F AES) and Flame Atomic Absorption Spectrometry (F AAS). The analytical method was optimized for the analysis of the analytes in liquid and powder samples, presenting a precision better than 4% and high accuracy, with recoveries between 95 and 103%. This latter indicated there is no significant matrix effects under established conditions. In addition, lower quantification limits were obtained in relation to the mineral concentrations in the samples: 306 and 782 mg kg-1 for Na and K (analyzed by F AES), and 2 and 246 mg kg-1 for Ca and Mg (determined via F AAS). The method was applied to the analysis of these minerals in organic raw milk from various certified farms in the southeast of Brazil, as well as in conventional milk from conventional farms located in Minas Gerais. The average concentrations found for organic milk were 390 mg kg-1 for Na, 1,099 mg kg-1 for K, 1,076 mg kg-1 for Ca and 76 mg kg-1 for Mg, while for conventional milk they were 420 mg kg-1 for Na, 1,161 mg kg-1 for K, 888 mg kg-1 for Ca and 79 mg kg-1 for Mg. These values varied according to the different management systems, influenced by intrinsic and extrinsic factors associated with milk production on the farms. However, in both cases the concentrations are in agreement with data found in the literature. Therefore, it can be concluded that the established method is suitable for monitoring the macrominerals Na, K, Ca and Mg in conventional and organic milk. In addition, it proved to be effective in determining these minerals in different forms of marketed milk (raw, UHT, pasteurized and powdered). These analytical characteristics allow the method to be used to evaluate the mineral composition of conventional and organic milk produced in Brazil.